The present invention refers to a process for making reinforced cellular materials from unsaturated polyester resins by injecting a liquid foam, made from said resins by mechanical introduction of a gas therein, into a closed molded containing the reinforcing materials which will be hereinafter specified.
The present invention also refers to the cellular materials thus obtained, as well as to the products made from said cellular materials.
Molded cellular materials of reinforced unsaturated polyester resins are known. Said materials however are obtained by impregnating the reinforcing material with an unsaturated polyester resin in liquid form, which resin is successively chemically expanded in the mold. Said process however has the following disadvantages:
the chemicals employed as foaming agents are usually toxic and further are generally unstable at room temperature and therefore must be maintained at low temperatures until their use; PA1 the process is not economical since the chemical foaming agent is expensive; PA1 the process requires molds suitably reinforced to stand the pressure produced during the expansion of the liquid resin.
A method for overcoming these disadvantages has been proposed in the art. It consists in carrying out the foaming by mechanical incorporation of the gas into the liquid resin. This method however does not permit to incorporate a reinforcing material having a length greater than 1.5 mm before the foaming stage, inasmuch as the mechanical devices for gas dispersion (nozzles and turbines) do not permit the passage of larger reinforcing materials and further such materials also cause a partial degradation of the foam.
A method for overcoming this last difficulty has also been proposed, which consists in separately preparing the foam by mechanical means and injecting it in liquid form into a closed mold in which a bed of dry fibres has been previously placed, which fibres are constituted by a mat of glass fibres cut and disposed over the entire cross-section of the mold or fixed on the two halves of the mold.
However, not even this method is free from disadvantages. Some of the disadvantages are:
(1) the styrene contained in the liquid resin dissolves the binder which keeps the mat together; (2) the entering flow of foam removes the glass fibres; (3) in the case of a mold containing the reinforcement in the form of a mat of glass fibres which are cut and disposed over all the cross-section of the mold, said reinforcement does not permit the foam to pass through without breaking it.